Orbi RBR850 Upload Speed Issue - ARP Table?

ISP came out and installed their WiFi Router - a Calix Gigaspire GS4220E between the RBR and the ONT device.  Nothing else has changed in my setup or configuration other than the insertion of the ISP router.  Both routers are on different private IP networks, Calix router has had the WiFi disabled.  Setup looks like this:

ONT --> ISP Router -->  RBR850 --> internal network

I have been doing hardwire speed tests ever since...and every single dang one has been 900 Mbps+ on both upload and download.   -_-  Just for fun I also did WiFi tests and the Wifi is achieving 500+Mpbs upload/download (as expected).

I cannot believe that the $700+ ORBI system is the cause of this problem (whatever the problem is... who knows).  But it is pretty cut-and-dry that the ISP router directly connected to the ONT device, re-routing all traffic through the ORBI can achieve full gigabit speeds but the ORBI by itself cannot.

I honestly don't know what I am going to do, I hate to walk away from a significant investment in my current ORBI setup but I can't accept that the ORBI is reducing upload speeds by 90%.